Automatic gain controller

ABSTRACT

Disclosed is an automatic gain controller capable of reducing signal saturation or signal distortion caused by out-of-band signals of a filter extracting an object signal or delay of a control signal and capable of precisely measuring a signal level in a filter band. An AGC response control section compares a level of control voltage (“V 2 _I terminal” signal) outputted from a first AGC control section and inputted into a “V 2 _I terminal” with a level of control voltage (“V 3 _I terminal” signal) outputted from a second AGC control section and inputted into a “V 3 _I terminal”. If the control voltage, which is the “V 3 _I terminal” signal, outputted from the second AGC control section is less than the control voltage, which is a “V 2 _I terminal” signal, outputted from the first AGC control section, the AGC response control section controls an AGC amplifier by using the control voltage outputted from the second AGC control section. If the control voltage, which is the “V 3 _I terminal” signal, outputted from the second AGC control section is greater than the control voltage, which is the “V 2 _I terminal” signal, outputted from the first AGC control section, the AGC response control section controls the AGC amplifier by using the control voltage outputted from the first AGC control section.

PRIORITY

[0001] This application claims priority to an application entitled“Automatic Gain Controller” filed in the Japanese Intellectual PropertyOffice on Mar. 6, 2003 and assigned Ser. No. 59764/2003, the contents ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an automatic gain controller.

[0004] 2. Description of the Related Art

[0005] In a conventional automatic gain controller having a filter in acontrol loop, an output signal of the conventional automatic gaincontroller is often interrupted due to a delay of responsecharacteristics thereof caused by a signal delay from the filter. Inorder to solve the above problem, a method has been proposed, wherein ifa signal level has a sudden variation, a control signal generator havinga rapid time constant is utilized to create a control signal to copewith a delay of the control signal caused by the filter, and at the sametime, control information is copied between the control signalgenerators in such a manner that an output signal of an automatic gaincontroller has no variation in level (referred to in Japanese Patent No.3,240,458).

[0006] In addition, in the conventional automatic gain controller havingthe filter in the control loop, if a level control of an automatic gaincontrol is carried out according to in-band signals of the filter, theautomatic gain control may be carried out to match levels of the in-bandsignals of the filter. Accordingly, if out-of-band signals of the filterare greater than in-band signals of the filter, saturation caused by theout-of-band signals of the filter may occur in an amplifier installed ata front end of the filter. For this reason, a method has been proposedin which amplifiers are cascade-connected through a filter and anautomatic gain control is separately carried out with respect to eachamplifier installed at front and rear portions of the filter (referredto in Japanese Patent No. 3,086,060).

[0007] Although above-described Japanese Patent Publication No.3,240,458 discloses a technique capable of solving a delay of responsecharacteristics caused by a signal delay from a filter and properlygenerating an output signal of an automatic gain controller, when alevel control of an automatic gain control is carried out according toin-band signals of the filter, saturation may occur in an amplifierinstalled at a front end of the filter caused by out-of-band signals ofthe filter, if out-of-band signals of the filter are greater thanin-band signals of the filter.

[0008] In addition, although above-described Japanese Patent PublicationNo. 3,086,060 can adjust a signal level at a front end of a filter bytracking variations of levels of out-of-band signals of the filter, ifan automatic gain control for the amplifier installed at the front endof the filter is carried out with a high-speed response according tovariation of out-of-band signals of the filter, unnecessary variationmay occur in the in-band object signals of the filter even though theobject signals are not subject to variation.

[0009] That is, if the automatic gain control for the amplifierinstalled at the front end of the filter is carried out with thehigh-speed response according to the variations of the signals, thein-band object signals of the filter may be subject to unnecessaryvariation, so the automatic gain control for the amplifier installed atthe rear end of the filter may be carried out according to thevariations of the object signals with a high-speed responsecharacteristic. However, if the automatic gain control with respect tothe object signals is carried out with the high-speed response, signalsmay be modulated due to the automatic gain control and signal distortionmay occur caused by an amplitude compression action of the automaticgain control.

[0010] Therefore, according to above-described Japanese Patentpublication No. 3,086,060, the automatic gain control for the amplifierinstalled at the front end of the filter must be carried out with alow-speed response according to the variations of out-of-band signals ofthe filter. In such a case, noise is generated by the out-of-bandsignals of the filter due to low response characteristics of theautomatic gain control. If the automatic gain control is carried out ata high-speed with respect to both amplifiers installed at front and rearends of the filter, distortion of the object signals may occur when theautomatic gain control is carried out with respect to the amplifierinstalled at the rear end of the filter, so communication quality willbe lowered.

SUMMARY OF THE INVENTION

[0011] Accordingly, the present invention has been made to solve theabove-mentioned problems occurring in the prior art, and an object ofthe present invention is to provide an automatic gain controller capableof reducing signal saturation or signal distortion caused by anout-of-band signal of a filter or a delay of a control signal, andprecisely measuring a level of an in-band signal of the filter.

[0012] In order to accomplish the above object, according to a firstaspect of the present invention, there is provided an automatic gaincontroller comprising: a first variable gain amplifying means, such asan AGC amplifier, for amplifying an input signal; a filter, such as anI-side channel filter or a Q-side channel filter, for limiting a band ofan output signal of the first variable gain amplifying means; a secondvariable gain amplifying means, such as an I-side amplifier or a Q-sideamplifier, for outputting an output signal of the filter by amplifyingthe output signal of the filter; a first control signal generatingmeans, such as a first AGC control section, generating a first controlsignal for controlling a level of the output signal of the firstvariable gain amplifying means to a predetermined level; a secondcontrol signal generating means, such as a second AGC control section,generating a second control signal for controlling a level of an outputsignal of the second variable gain amplifying means to a predeterminedlevel and outputting the second control signal to the second variablegain amplifying means; and a control signal selecting means, such as anAGC response control section, selecting one of the first and secondcontrol signals generated from the first and second control signalgenerating means and outputting a selected control signal to the firstvariable gain amplifying means.

[0013] According to the automatic gain controller having the abovestructure, the control signal selecting means selects one of the firstand second control signals generated from the first and second controlsignal generating means in order to control the first variable gainamplifying means. Thus, the first variable gain amplifying meansinstalled at the front end of the filter can be controlled based onvariations of a signal inputted into the filter or based on variationsof a signal outputted from the filter, so out-of-band signals of thefilter may not exert an influence when a gain control is carried out.

[0014] In addition, according to a second aspect of the presentinvention, there is provided an automatic gain controller comprising: afirst variable gain amplifying means, such as an AGC amplifier, foramplifying an input signal; a filter, such as an I-side channel filteror a Q-side channel filter, for limiting a band of an output signal ofthe first variable gain amplifying means; a second variable gainamplifying means, such as an AGC amplifier, for amplifying an outputsignal of the filter; a third variable gain amplifying means, such as anI-side AGC amplifier, a Q-side AGC amplifier or an AGC amplifier, foroutputting the output signal of the filter by amplifying the outputsignal of the filter; a first control signal generating means, such as afirst AGC control section, generating a first control signal forcontrolling a level of the output signal of the first variable gainamplifying means to a predetermined level; a second control signalgenerating means, such as a second AGC control section, generating asecond control signal for controlling a level of an output signal of thesecond variable gain amplifying means to a predetermined level andoutputting the second control signal to the second variable gainamplifying means; a third control signal generating means, such as athird AGC control section, having a response characteristic faster thana response characteristic of the second control signal generating means,generating a third control signal for controlling a level of an outputsignal of the third variable gain amplifying means to a predeterminedlevel, and outputting the third control signal to the third variablegain amplifying means; and a control signal selecting means, such as anAGC response control section, selecting one of the first and secondcontrol signals generated from the first and second control signalgenerating means and outputting a selected control signal to the firstvariable gain amplifying means.

[0015] According to the automatic gain controller having the abovestructure, the control signal selecting means selects one of the firstcontrol signal generated from the first control signal generating meansand the second control signal, which is generated from the secondcontrol signal generating means independent from the controller, inorder to control the first variable gain amplifying means. Thus, thefirst variable gain amplifying means installed at the front end of thefilter can be controlled based on variation of a signal inputted intothe filter or based on variations of a signal outputted from the filterindependent from the output signal of the controller, so out-of-bandsignals of the filter may not exert an influence when a gain control iscarried out.

[0016] According to a third aspect of the present invention, each of thesecond and third control signal generating means includes a controlinformation copying unit for copying control information of the secondcontrol signal generating means into the third control signal generatingmeans when the control signal selecting means selects the second controlsignal generated from the second signal generating means and outputs thesecond control signal to the first variable gain amplifying means.

[0017] In the automatic gain controller having the above structure, whenthe first variable gain amplifying means installed at the front end ofthe filter is controlled based on variations of the signal outputtedfrom the filter by using the second control signal generating means,control information of the second control signal generating means iscopied into the third control signal generating means. In addition, again control is carried out with respect to the first, second and thirdvariable gain amplifying means in accordance with a response speed ofthe second control signal generating means based on variations of thesignal outputted from the filter. Thus, it is possible to prevent thethird control signal generating means from being controlled with anunnecessarily high response speed while preventing the output signal ofthe controller from being distorted.

[0018] According to a fourth aspect of the present invention, thecontrol information copying unit copies control information of thesecond control signal generating means into the third control signalgenerating means, when a variation value of the first control signalgenerated from the first control signal generating means per a unit timeis less than a predetermined value.

[0019] According to the automatic gain controller having the abovestructure, since a strong signal out of a filter band may exist, thevariation value of the first control signal generated from the firstcontrol signal generating means per a unit time is less than thepredetermined value even if the control signal selecting means selectsthe first control signal and outputs the first control signal to thefirst variable gain amplifying means. In addition, the controlinformation copying unit copies control information of the secondcontrol signal generating means into the third control signal generatingmeans if it matches with the response characteristic for controlling thesecond variable gain amplifying means. In contrast, if the variationvalue of the first control signal per a unit time is greater than thepredetermined value, the control information copying unit cannot copycontrol information. Thus, it is possible to prevent the output signalof the controller from being distorted, which is caused by a rapidresponse characteristic for the third variable gain amplifying meanswhen gain variation of the first variable gain amplifier is small. Inaddition, when gain variation of the first variable gain amplifier isgreat, the response characteristic for the third variable gainamplifying means is not dependent on the gain variation, so the outputsignal of the controller is prevented from being distorted.

[0020] According to a fifth aspect of the present invention, the controlsignal selecting means compares the first control signal of the firstcontrol signal generating means with the second control signal of thesecond control signal generating means, and at the same time, selectsone of the first and second control signals capable of lowering a gainof the first variable gain amplifying means, and outputs the selectedsignal to the first variable gain amplifying means.

[0021] The automatic gain controller having the above structure caneasily select the control signal outputted to the first variable gainamplifying means by comparing the control signals with each other.

[0022] According to a sixth aspect of the present invention, a referencevalue varying means is provided for varying a reference value, which iscompared with a level of an input signal, depending on a status ofquality information, when quality information of a received signal isobtained from a signal demodulation section connected to a rear end ofthe automatic gain controller and when the first control signalgenerating means generates the first control signal based on a level ofthe input signal.

[0023] According to the automatic gain controller having the abovestructure, it is possible to balance the influence of an out-of-bandsignal and the in-band signal of the filter when gain control is carriedout with respect to the in-band signal of the filter.

[0024] According to a seventh aspect of the present invention, thereference value varying means varies the reference value by comparing alevel of the first control signal generated from the first controlsignal generating means with a level of the second control signalgenerated from the second control signal generating means, and bycomparing a level of a received in-band signal with a predeterminedvalue.

[0025] In the automatic gain controller having the above structure, if alevel of the second control signal generated from the second controlsignal generating means is lower than a level of the first controlsignal generated from the first control signal generating means, and atthe same time, a level of a received in-band signal is below apredetermined level, the reference value varying means varies thereference value so as to raise the level of the output signal of thefirst variable gain amplifying means. In addition, if the level of thesecond control signal generated from the second control signalgenerating means is lower than the level of the first control signalgenerated from the first control signal generating means, and at thesame time, the level of the received in-band signal is higher than thepredetermined level, the reference value varying means varies thereference value so as to lower the level of the output signal of thefirst variable gain amplifying means. Thus, if a desired signalreceiving performance is not achieved, a reason thereof can be found byusing the level of the received signal, so proper control may be carriedout corresponding to the reason.

[0026] According to an eighth aspect of the present invention, a gaindistribution adjusting means is provided to adjust a gain distributionin a front end circuit and a rear end circuit of the filter by comparinga level of an out-of-band signal of the filter with a level of anin-band signal of the filter.

[0027] The automatic gain controller having the above structure canproperly determine the gain distribution in front and rear portions ofthe filter by comparing the signal levels of an out-of-band signal andan in-band signal of the filter with each other.

[0028] According to a ninth aspect of the present invention, a signalstrength calculating means, such as a comparator, a switch, asubtractor, a variable gain amplifier, or an adder of the AGC responsecontrol section, is provided. If the first control signal generated fromthe first control signal generating means is control voltage V3, and thesecond control signal generated from the second control signalgenerating means is control voltage V1, and at the same time, if anoverall gain characteristic with respect to the control voltage V1 isG(V1) and a gain characteristic of a front circuit of the filter withrespect to the control voltage V1 is G3(V1), the signal strengthcalculating means determines the control voltage V1 as a strength of anin-band signal of the filter when the control voltage V3 is greater thanthe control voltage V1, and determines a calculating value V as thestrength of the in-band signal of the filter when the control voltage V3is less than the control voltage V1, wherein the calculating value Vsatisfies the following Equation 1:

V=V 1+(G 3(V 1)/G(V 1))(V 1−V 3)

[0029] The automatic gain controller having the above structure caneasily measure the object signal level by using control signalsgenerated from each control signal generating means.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above object and other features and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

[0031]FIG. 1 is a block diagram showing a structure of a wirelessapparatus having an automatic gain controller (AGC) according to a firstembodiment of the present invention;

[0032]FIG. 2 is a block diagram showing a structure of an AGC detector(complex input) of an automatic gain controller according to the firstembodiment of the present invention;

[0033]FIG. 3 is a block diagram showing a structure of an AGC controlsection according to the first embodiment of the present invention;

[0034]FIG. 4 is a block diagram showing a structure of an AGC responsecontrol section of an automatic gain controller according to the firstembodiment of the present invention;

[0035]FIG. 5 is a block diagram showing a structure of an AGC responsecontrol section of an automatic gain controller according to the firstembodiment of the present invention;

[0036]FIG. 6 is a graph showing an example of a gain characteristic ofan AGC amplifier as a function of control voltage when the AGC amplifieris installed at a rear end of a channel filter of an automatic gaincontroller according to the first embodiment of the present invention;

[0037]FIG. 7 is a graph showing an example of a gain characteristic ofan AGC amplifier as a function of control voltage when the AGC amplifieris installed at a front end of a channel filter of an automatic gaincontroller according to the first embodiment of the present invention;

[0038]FIG. 8 is a graph showing an example of a function FN(x)characteristic in a function block of an automatic gain controlleraccording to the first embodiment of the present invention;

[0039]FIG. 9 is a block diagram showing a structure of a wirelessapparatus having an AGC according to a second embodiment of the presentinvention;

[0040]FIG. 10 is a block diagram showing a structure of an AGC detector(real input) of an automatic gain controller according to the secondembodiment of the present invention;

[0041]FIGS. 11A to 11K are views showing a response waveform in eachpart of an automatic gain controller according to the second embodimentof the present invention;

[0042]FIG. 12 is a block diagram showing a structure of a wirelessapparatus having an AGC according to a third embodiment of the presentinvention;

[0043]FIG. 13 is a block diagram showing a structure of a wirelessapparatus having an AGC according to a fourth embodiment of the presentinvention;

[0044]FIG. 14 is a graph showing an example of a gain characteristic ofan AGC amplifier as a function of control voltage when the AGC amplifieris installed at a rear end of a channel filter of an automatic gaincontroller according to a fifth embodiment of the present invention; and

[0045]FIG. 15 is a graph showing an example of a gain characteristic ofan AGC amplifier as a function of control voltage when the AGC amplifieris installed at a front end of a channel filter of an automatic gaincontroller according to the fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0046] Hereinafter, preferred embodiments of the present invention willbe described with reference to the accompanying drawings. In thefollowing description of the present invention, a detailed descriptionof known functions and configurations incorporated herein will beomitted when it may obscure the subject matter of the present invention.

Embodiment 1

[0047] First, an automatic gain controller according to a firstembodiment of the present invention will be described.

[0048] A. Structure

[0049]FIG. 1 is a block diagram showing a structure of a wirelessapparatus having an automatic gain controller (AGC) according to thefirst embodiment of the present invention. Referring to FIG. 1, a signalinputted into a mixer 1 from an RF/IF terminal is converted into asignal having a low frequency (input IF frequency of A/D converter 5,which will be described later) in the mixer 1 by using a local signalhaving a first frequency, which is outputted from a local oscillator 2.Then, a signal having a predetermined frequency band is extracted fromthe signal outputted from the mixer by using a bandpass filter 3.

[0050] An AGC amplifier 4 is a variable gain amplifier for converting anoutput signal of the bandpass filter 3 into a signal having a constantlevel. The signal having the predetermined frequency band, which isconverted into the signal having the constant level by the AGC amplifier4, is inputted into the A/D converter 5 so that the signal is convertedinto a quantizing digital signal by means of the A/D converter 5.

[0051] In addition, an orthogonal detection is carried out with respectto the quantizing digital signal by using a local signal (cosine wave inI-side and −sine wave in Q-side) having a second frequency outputtedfrom a digital local oscillator 8 of an I-side mixer 6 and a Q-sidemixer 7 and is converted into a complex number signal having a basebandfrequency represented by an I-axis signal and a Q-axis signal.

[0052] The complex number signal having the baseband frequency isinputted into an AGC detector 9. At the same time, the complex numbersignal is converted into a band signal of an objective band, due tobands of the I-axis signal and the Q-axis signal of the complex numbersignal being limited by an I-side channel filter 10 and a Q-side channelfilter 11, respectively. In addition, the I-axis signal and the Q-axissignal are inputted into an I-side amplifier 12 and a Q-side amplifier13, respectively. Since the AGC detector 9 generates a gain controlsignal for the AGC amplifier 4, the AGC detector 9 calculates squarevalues of the I-axis signal and the Q-axis signal of the complex numbersignal having the baseband frequency and a square root value of thecomplex number signal. Variation of an output signal of the I-side mixer6 and the Q-side mixer 7 is detected by integrating the square rootvalue of the complex number signal.

[0053] In addition, I-side AGC amplifier 12 and Q-side AGC amplifier 13are variable gain amplifiers for converting output signals of the I-sidechannel filter 10 and the Q-side channel filter 11 into signals havingconstant levels. Band signals of the objective bands, which areconverted into signals having constant levels by the I-side AGCamplifier 12 and the Q-side AGC amplifier 13, are complex number signalsBB.I and BB.Q having baseband frequencies, which are outputted from thewireless apparatus.

[0054] The band signals of the objective bands, which are converted intosignals having constant levels by the I-side AGC amplifier 12 and theQ-side AGC amplifier 13, are inputted into an AGC detector 14. Since theAGC detector 14 generates a gain control signal for the I-side AGCamplifier 12 and the Q-side AGC amplifier 13, the AGC detector 14calculates square values of the I-axis signal and the Q-axis signal ofthe band signals of the objective bands and square root values of theband signals. Variation of an output signal of the I-side AGC amplifier12 and the Q-side AGC amplifier 13 is detected by integrating the squareroot values of the band signals.

[0055] In the same manner, bands of an I-axis signal and a Q-axis signalof the band signals of the objective bands are limited by the I-sidechannel filter 10 and the Q-side channel filter 11, respectively. Inaddition, the I-axis signal and the Q-axis signal are inputted into anI-side amplifier 15 and a Q-side amplifier 16, respectively. The I-sideamplifier 15 and the Q-side amplifier 16 are variable gain amplifiersfor converting output signals of the I-side channel filter 10 and theQ-side channel filter 11 into signals having constant levels. The bandsignals of the objective bands, which are converted into signals havingconstant levels by the I-side amplifier 15 and the Q-side amplifier 16,are inputted into an AGC detector 17.

[0056] In order to generate a gain control signal for the I-sideamplifier 15 and the Q-side amplifier 16, the AGC detector calculatessquare values of the I-axis signal and the Q-axis signal of the bandsignals of the objective bands and square root values of the bandsignals. Variation of an output signal of the I-side amplifier 15 andthe Q-side amplifier 16 is detected by integrating the square rootvalues of the band signals.

[0057] The AGC detectors 9, 14 and 17 will be described in detail later.

[0058] The output signals of the AGC detectors 9, 14 and 17 are comparedwith reference values thereof in order to generate gain control signalsfor each amplifier. Comparative data are inputted into an AGC controlsection for generating the gain control signal for each amplifier. Indetail, a reference value Ref3 outputted from a reference value register18 is subtracted from an output signal of the AGC detector 9 by means ofa subtractor 19 and a result thereof is inputted into an “In terminal”of an AGC control section 20.

[0059] In addition, a reference value Ref1 outputted from a referencevalue register 21 is subtracted from an output signal of the AGCdetector 14 by means of a subtractor 22 and a result thereof is inputtedinto an “In terminal” of an AGC control section 23. Also, the referencevalue Ref1 outputted from the reference value register 21 is subtractedfrom an output signal of the AGC detector 17 by means of a subtractor 24and a result thereof is inputted into an “In terminal” of an AGC controlsection 25 having response characteristics slower than responsecharacteristics of the AGC control section 23.

[0060] Herein, the AGC control sections 20, 23 and 25 multiply inputsignals inputted into “In terminals” by a coefficient selected based oncontrol signals inputted into “C_sw terminals” and output a resultthereof to “Out terminals”. In addition, the AGC control sections 20, 23and 25 copy control information from “Reg_Out terminals” to “Reg_Interminals” based on control signals inputted into “Reg_Ld terminals”.Referring to FIG. 1, the “Reg_Out terminal” of the AGC control section25 is connected to the “Reg_In terminal” of the AGC control section 23,and control information of the AGC control section 25 is copied in theAGC control section 23 based on a control signal inputted into the“Reg_Ld terminal” of the AGC control section 23 from a signal outputfrom the “Reg_Ld terminal” of AGC response control section 26.

[0061] The AGC control sections 20, 23 and 25 will be described indetail later. In the following description, functions of terminals whichare not connected to the AGC control sections 20, 23 and 25 will not bediscussed.

[0062] The “Out terminal” of the AGC control section 23 is connected toa “V1_I terminal” of AGC response control section 26 and gain controlterminals of the I-side AGC amplifier 12 and the Q-side AGC amplifier 13in such a manner that gains of the I-side AGC amplifier 12 and theQ-side AGC amplifier 13 can be controlled by means of an output signalof the “Out terminal” of the AGC control section 23. In addition, the“Out terminal” of the AGC control section 25 is connected to a “V2_Iterminal” of the AGC response control section 26 and gain controlterminals of the I-side AGC amplifier 15 and the Q-side AGC amplifier 16in such a manner that gains of the I-side AGC amplifier 15 and theQ-side AGC amplifier 16 can be controlled by means of an output signalof the “Out terminal” of the AGC control section 25. The “Out terminal”of the AGC control section 20 is connected to a “V3_I terminal” of theAGC response control section 26.

[0063] AGC response control section 26 is a control section forcontrolling response characteristics of each AGC control section andgenerating a gain control signal for the AGC amplifier 4. In detail, asignal created by subtracting the reference value Ref3 of the referencevalue register 18 from the output signal of the AGC detector 9 in thesubtractor 19 is inputted into a “Wdet_I terminal” of the AGC responsecontrol section 26. In the same manner, a signal created by subtractingthe reference value Ref1 of the reference value register 21 from theoutput signal of the AGC detector 14 in the subtractor 22 is inputtedinto an “Fdet_I terminal” of the AGC response control section 26. Inaddition, a signal created by subtracting the reference value Ref1 ofthe reference value register 21 from the output signal of the AGCdetector 17 in the subtractor 24 is inputted into an “Sdet_I terminal”of the AGC response control section 26.

[0064] Meanwhile, a “C1_O terminal” of the AGC response control section26 is connected to a “C_sw terminal” of the AGC control section 23, a“C2_O terminal” of the AGC response control section 26 is connected to a“C_sw terminal” of the AGC control section 25 and a “C3_O terminal” ofthe AGC response control section 26 is connected to a “C_sw terminal” ofthe AGC control section 20. In addition, the “Reg_Ld terminal” of theAGC response control section 26 is connected to the “Reg_Ld terminal” ofthe AGC control section 23 so as to control the copying of the controlsignal from the AGC control section 25 to the AGC control section 23.

[0065] A “Va_O” terminal of the AGC response control section 26 outputsa gain control signal for the AGC amplifier 4. The gain control signaloutputted from the “Va_O” terminal of the AGC response control section26 is converted into an analog signal by means of a D/A converterthrough a function block 27 capable of finely adjusting responsecharacteristics of the automatic gain controller according to thepresent invention and is inputted into a gain control terminal of theAGC amplifier 4. The AGC response control section 26 will be describedin detail later.

[0066] In addition, the wireless apparatus includes a controller (notshown) controlling the function block 27 and updating reference valuesof each reference value register and internal register valuesdetermining the response characteristic of each AGC control section.

[0067] B. AGC Detector

[0068] Hereinafter, AGC detectors 9, 14 and 17 of the automatic gaincontroller according to the first embodiment of the present inventionwill be described in detail with reference to accompanying drawings. TheAGC detectors 9, 14 and 17 have the same structure as each other, andFIG. 2 shows a structure of a complex input type AGC detector.

[0069] Referring to FIG. 2, as a complex signal is inputted through an“In.I terminal” and an “In.Q terminal”, an amplitude calculator 101calculates square values of an I-axis signal and a Q-axis signal andadds the square values to the complex signal. At the same time, a squareroot value of the complex signal is calculated. An output signal of theamplitude calculator 101 is simultaneously inputted into a comparator102 and an integrator 103 including a multiplier 103 a, an adder 103 b,a delay unit 103 c, a multiplier 103 d, and a coefficient calculator 103e.

[0070] Herein, the integrator 103 integrates an output signal of theamplitude calculator 101 based on any one of an attack coefficientoutputted from an attack coefficient register 105 and a releasecoefficient outputted from a release coefficient register 106 (wherein,an attack coefficient value is larger than a release coefficient value),which are selected by a switch 104 controlled by means of an outputsignal of the comparator 102. In detail, the output signal of theamplitude calculator 101 inputted into the integrator 103 is multipliedby one of the attack coefficient and the release coefficient, which areinputted into the integrator 103 as numerator coefficients, by means ofthe multiplier 103 a.

[0071] In addition, a denominator coefficient of the attack coefficientor the release coefficient inputted into the integrator 103 iscalculated by means of the coefficient calculator 103 e. An outputsignal of the coefficient calculator 103 e is multiplied by an outputsignal of the integrator 103 through the multiplier 103 d and the resultis added to an output signal of the multiplier 103 a by means of theadder 103 b. Meanwhile, an output signal of the adder 103 b is outputtedthrough an “Out terminal” via the delay unit 103 c as an output signalof the integrator 103, that is, as an output signal of the AGC detector.

[0072] The comparator 102 compares the output signal of the amplitudecalculator 101 with an output signal of the multiplier 103 d. If theoutput signal of the amplitude calculator 101 is smaller than the outputsignal of the multiplier 103 d, the switch 104 selects the releasecoefficient so as to enlarge an integrate time constant. If the outputsignal of the amplitude calculator 101 is larger than the output signalof the multiplier 103 d, the switch 104 selects the attack coefficientso as to reduce the integration time constant. Thus, the value of theoutput signal of the integrator 103 may be between an effective valueand a peak value of an input signal.

[0073] C. AGC Control Section

[0074] Hereinafter, AGC control sections 20, 23, and 25 of the automaticgain controller according to the first embodiment of the presentinvention will be described in detail with reference to accompanyingdrawings. The AGC control sections 20, 23 and 25 have the same structureas each other. FIG. 3 is a block diagram showing the structure of theAGC control section of the automatic gain controller.

[0075] Referring to FIG. 3, an input signal inputted through an “Interminal” is multiplied by any one of an attack coefficient and arelease coefficient (wherein, an attack coefficient value is larger thana release coefficient value) through a multiplier 204, in which therelease coefficient is outputted from a release coefficient register 203and the attack coefficient is outputted from an attack coefficientregister 202 according to a selection of a switch 201 which iscontrolled based on a control signal inputted into a “C_sw terminal”.

[0076] In addition, an output signal of the multiplier 204 is subtractedfrom an output signal of the AGC control section by means of asubtractor 205 and inputted into a switch 206.

[0077] The switch 206 selects any one of an output signal of thesubtractor 205 and an input signal inputted into an “Reg_In terminal”based on a control signal inputted into an “Reg_Ld terminal”. Theselected signal is outputted through a “Reg_Out terminal” and isinputted into a delay unit 207. In addition, an output signal of thedelay unit 207 is outputted through an “Out terminal” as an outputsignal of the AGC control section.

[0078] The switch 201 selects the attack coefficient outputted from theattack coefficient register 202 if the control signal inputted into the“C-sw terminal” is “0” and selectively outputs the release coefficientoutputted from the release coefficient register 203 if the controlsignal inputted into the “C-sw terminal” is “1”.

[0079] In addition, the switch 206 selects the output signal of thesubtractor 205 if the control signal inputted into the “Reg_Id terminal”is “0” and selectively outputs an input signal inputted into the “Reg_Interminal” if the control signal inputted into the “Reg-Ld terminal” is“1”.

[0080] D. AGC Response Control Section

[0081] Hereinafter, the AGC response control sections 26 of theautomatic gain controller according to the first embodiment of thepresent invention will be described in detail with reference toaccompanying drawings. FIGS. 4 and 5 are block diagrams showing astructure of the AGC response control section of the automatic gaincontroller according to a first embodiment of the present invention.

[0082] Referring to FIGS. 4 and 5, signals inputted through the “V2_Iterminal” and the “V3_I terminal” are compared with each other by meansof a comparator 301. At the same time, one of the signals inputtedthrough the “V2_I terminal” and the “V3_I terminal” is selected by aswitch 302, which is controlled and switched by means of an outputsignal of the comparator 301, and the selected signal is outputted tothe “Va_O terminal”.

[0083] In addition, if the signal inputted into the “V3_I terminal” islower than the signal inputted into the “V2_I terminal”, the comparator301 outputs “0”, and the switch 302 outputs the signal inputted into the“V3_I terminal” through the “Va_O terminal”.

[0084] If the signal inputted into the “V3_I terminal” is larger thanthe signal inputted into the “V2_I terminal”, the comparator 301 outputs“1”, and the switch 302 outputs the signal inputted into the “V2_Iterminal” through the “Va_O terminal”.

[0085] In addition, an output signal of the switch 302 is delayed by adelay unit 303. At the same time, the output signal of the switch 302delayed by the delay unit 303 is differentiated by subtracting theoutput signal of the switch 302 from the delayed output signal of theswitch 302 by means of a subtractor 304. In addition, an absolute valueof the output signal of the switch 302 is calculated by means of anabsolute value calculator 305.

[0086] An output signal of the absolute value calculator 305 is inputtedinto an integrator 306 including a multiplier 306 a, an adder 306 b, adelay unit 306 c, a multiplier 306 d and a coefficient calculator 306 e.

[0087] Herein, the integrator 306 is designed to integrate the outputsignal of the absolute value calculator 305 based on a “Va Deltaintegral coefficient” outputted from a Va Delta integral coefficientregister 307. In detail, the output signal of the absolute valuecalculator 305 inputted into the integrator 306 is multiplied by the “VaDelta integral coefficient” inputted into the integrator 306 as anumerator coefficient of the integrator by means of the multiplier 306a.

[0088] In addition, a denominator coefficient of the “Va Delta integralcoefficient” inputted into the integrator 306 is calculated by means ofthe coefficient calculator 306 e. An output signal of the coefficientcalculator 306 e is multiplied by the output signal of the integrator305 by means of the multiplier 306 d and a result thereof is added to anoutput signal of the multiplier 306 a by means of the adder 306 b. Anoutput signal of the adder 306 b passes through the delay unit 306 andis outputted as an output signal of the integrator 306. Accordingly, avariation degree of a signal outputted to the “Va_O terminal” can becalculated.

[0089] The output signal of the integrator 306 is inputted into acomparator 308 so that the output signal of the integrator 306 iscompared with a reference value “Va Delta Ref.” outputted from a Vareference value register 309. The comparator 308 outputs “1” if theoutput signal of the integrator 306, that is the variation degree of thesignal outputted to the “Va_O terminal” is smaller than the referencevalue “Va Delta Ref”.

[0090] Meanwhile, a logical sum (OR) of the output signals of thecomparators 301 and 308 is obtained from an OR circuit 310 and isinputted into an AND circuit 311 located in front of the OR circuit 310.Thus, if the signal inputted into the “V3_I terminal” is larger than thesignal inputted into the “V2_I terminal”, or if the variation degree ofthe signal outputted to the “Va_O terminal” is smaller than thereference value “Va Delta Ref.”, “1” is inputted into the AND circuit311.

[0091] In addition, the signal inputted through the “V2_I terminal” issubtracted from the signal inputted through the “V1_I terminal” by meansof a subtractor 312. At the same time, an output signal of thesubtractor 312 is inputted into an absolute value calculator 313 so thatan absolute value of the output signal of the subtractor 312 iscalculated. In addition, an output signal of the absolute valuecalculator 313 is inputted into a comparator 314 so that the outputsignal of the absolute value calculator 313 is compared with a referencevalue “V1 V2 Diff Ref ” outputted from a V1−V2 differential valueregister 315.

[0092] If an absolute value of a differential value between the signalinputted into the “V1_I terminal” and the signal inputted into the “V2_Iterminal” is lower than the reference value “V1 V2 Diff Ref”, an outputsignal of the comparator 314 becomes “1” and “1” is inputted into theAND circuit 311. In addition, if the absolute value of the differentialvalue between the signal inputted into the “V1_I terminal” and thesignal inputted into the “V2_I terminal” is larger than the referencevalue “V1 V2 Diff Ref”, the output signal of the comparator 314 becomes“0” and “0” is inputted into the AND circuit 311.

[0093] Meanwhile, the signal inputted into the “Sdet_I terminal” iscompared with a reference value “Slow Ref+” outputted from a register318 capable of checking an upper limit value of a control signal bymeans of a comparator 316, and is compared with a reference value “SlowRef−” outputted from a register 319 capable of checking a lower limitvalue of a control signal by means of a comparator 317. In addition,output signals of the comparators 316 and 317 are inputted into the ANDcircuit 311 via an AND circuit 320.

[0094] In addition, the output signal of the comparator 316 becomes “1”if the signal inputted into the “Sdet_I terminal” is lower than thereference value “Slow Ref+” and the output signal of the comparator 317becomes “1” if the signal inputted into the “Sdet_I terminal” is greaterthan the reference value “Slow Ref−”, “1” is inputted into the ANDcircuit 311 via the AND circuit 320 if the signal inputted into the“Sdet_I terminal” is in a range between the reference value “Slow Ref+”and the reference value “Slow Ref−”.

[0095] The output signal of the comparator 316 becomes “0” if the signalinputted into the “Sdet_I terminal” is greater than the reference value“Slow Ref+” and the output signal of the comparator 317 becomes “0” ifthe signal inputted into the “Sdet_I terminal” is lower than thereference value “Slow Ref−”, “0” is inputted into the AND circuit 311via the AND circuit 320.

[0096] In addition, a logical multiply (AND) of the output signals ofthe OR circuit 310 and the comparators 314 and 320 is obtained from theAND circuit 311 and an output signal of the AND circuit 311 is outputtedto the “Reg_Ld terminal”.

[0097] The signal inputted into the “Fdet_I terminal” is compared with areference value “0” outputted from a zero register 322 by means of acomparator 321. At this time, if the signal inputted into the “Fdet_Iterminal” is below the reference value “0”, an output signal of thecomparator 321 becomes “1” and is outputted to the “C1_O terminal”. Inaddition, if the signal inputted into the “Fdet_I terminal” is greaterthan the reference value “0”, the output signal of the comparator 321becomes “0” and is outputted to the “C1_O terminal”.

[0098] The signal inputted into the “Sdet_I terminal” is compared withthe reference value “0” outputted from the zero register 322 by means ofa comparator 323. At this time, if the signal inputted into the “Sdet_Iterminal” is below the reference value “0”, an output signal of thecomparator 323 becomes “1” and is outputted to the “C2_O terminal”. Inaddition, if the signal inputted into the “Sdet_I terminal” is greaterthan the reference value “0”, the output signal of the comparator 323becomes “0” and is outputted to the “C2_O terminal”.

[0099] In addition, the signal inputted into the “Wdet_I terminal” iscompared with the reference value “0” outputted from the zero register322 by means of a comparator 324. At this time, if the signal inputtedinto the “Wdet_I terminal” is below the reference value “0”, an outputsignal of the comparator 324 becomes “1” and is outputted to the “C3_Oterminal”. In addition, if the signal inputted into the “Wdet_Iterminal” is greater than the reference value “0”, the output signal ofthe comparator 324 becomes “0” and is outputted to the “C3_O terminal”.

[0100] The signals inputted into the “V1_I terminal” and the “V3_Iterminal” are compared with each other by means of a comparator 325. Atthe same time, the signal inputted into the “V1_I terminal” or a signal,which is created by compensating for the signal inputted into the “V1_Iterminal” by using the signal inputted into the “V3_I terminal”, isselected by a switch 326 which is controlled and switched by means of anoutput signal of the comparator 325. Then, the selected signal isoutputted as an RSSI (Received Signal Strength Indicator) signal throughan “RSSI terminal”.

[0101] When the signal inputted into the “V3_I terminal” is greater thanthe signal inputted into the “V1_I terminal”, the output signal of thecomparator 325 becomes “1”, so the switch 326 outputs the signalinputted into the “V1_I terminal” through the “RSSI terminal”. Inaddition, if the signal inputted into the “V3_I terminal” is smallerthan the signal inputted into the “V1_I terminal”, the output signal ofthe comparator 325 becomes “0”, so the switch 326 outputs the signal,which is created by compensating for the signal inputted into the “V1_Iterminal” by using the signal inputted into the “V3_I terminal”, throughthe “RSSI terminal”.

[0102] In addition, following Equation 2 can be obtained in order tocompensate for the signal inputted into the “V1_I terminal” by using thesignal inputted into the “V3_I terminal”, in which signals of eachterminal are represented as terminal names.

“RSSI”=“V 1_I”+(G 3(V 1)/G(V 1))(“V 1_I”−“V 3_I”).  Equation 2

[0103] In detail, (“V1_I”−“V3_I”) is calculated by a subtractor 327, anoutput signal of the subtractor 327 is multiplied by a coefficient(G3(V1)/G(V1)) by means of a variable gain amplifier 328, and “V1_I” isadded thereto by means of an adder 329, thereby obtaining the aboveequation.

[0104] E. Characteristic of AGC Amplifiers

[0105] Hereinafter, the characteristic of the AGC amplifiers used in theautomatic gain controller according to the first embodiment of thepresent invention will be described with reference to accompanyingdrawings.

[0106]FIG. 6 is a graph showing an example of a gain characteristic as afunction of control voltage in the I-side AGC amplifier 12, Q-side AGCamplifier 13, I-side AGC amplifier 15, and Q-side AGC amplifier 16.According to the characteristic of each AGC amplifier, the gain isconstantly maintained at −25 [dB] when the control voltage is below 0.0,and is constantly maintained at −25 [dB] when the control voltage isabove 1.0. When the control voltage is in a range between 0.0 and 1.0,the gain increases by 5 [dB] as the control voltage increases by 0.1. Inaddition, the gain becomes 0 [dB] when the control voltage becomes 0.5.

[0107]FIG. 7 is a graph showing an example of a gain characteristic as afunction of control voltage in the AGC amplifier 4. According to thecharacteristic of the AGC amplifier 4, a gain is constantly representedas −35 [dB] when the control voltage is below 0.0 and is constantlyrepresented as 15 [dB] when the control voltage is above 1.0. Inaddition, when the control voltage is in a range between 0.0 and 1.0,the gain increases by 5 [dB] as the control voltage increases by 0.1.Meanwhile, the gain becomes 0 [dB] when the control voltage becomes 0.7.

[0108] F. Operation of Automatic Gain Controller

[0109] Hereinafter, an operation of the automatic gain controller havingthe above-mentioned structure according to the first embodiment of thepresent invention will be described. The automatic gain controller ofthe present invention includes a first AGC loop and a second AGC loopinstalled at rear ends of the I-side channel filter 10 and the Q-sidechannel filter 11, respectively. The first AGC loop includes the I-sideAGC amplifier 12, the Q-side AGC amplifier 13, the AGC detector 14 andthe AGC control section 23 and performs a high-speed response. Thesecond AGC loop includes the I-side AGC amplifier 15, the Q-side AGCamplifier 16, the AGC detector 17 and the AGC control section 25 andperforms a low-speed response with a low signal distortion. An outputsignal of the automatic gain controller is extracted from the first AGCloop.

[0110] In addition, a third AGC loop including the AGC amplifier 4, theAGC detector 9, and the AGC control section 20 is installed at frontends of the I-side channel filter 10 and the Q-side channel filter 11 inorder to detect an overall signal level before out-of-band signals ofobjective bands are restricted by the I-side channel filter 10 and theQ-side channel filter 11.

[0111] At this time, the AGC response control section 26 controls theAGC amplifier 4, by means of control voltage outputted from the AGCcontrol section 20, if the overall signal level before the out-of-bandsignals of the objective bands are restricted is larger than apredetermined value, in such a manner that the AGC response controlsection 26 may control the AGC amplifier 4 only when the overall signallevel exceeds the predetermined value, by considering the bands of theI-side channel filter 10 and the Q-side channel filter 11 and theoverall signal level inputted into the automatic gain controller.Meanwhile, if the overall signal level before the out-of-band signals ofthe objective bands are restricted is lower than the predeterminedvalue, the AGC response control section 26 controls the AGC amplifier 4by means of control voltage outputted from the AGC control section 25.

[0112] In detail, a level of the control voltage outputted from the AGCcontrol section 25 and inputted into the “V2_I terminal” is comparedwith a level of the control signal outputted from the AGC controlsection 20 and inputted into the “V3_I terminal” by means of the AGCresponse control section 26. In addition, the AGC response controlsection 26 controls the AGC amplifier 4 by using the control voltage(“V3_I terminal signal) outputted from the AGC control section 20, ifthe control voltage (“V3_I terminal signal) outputted from the AGCcontrol section 20 is lower than the control voltage (“V2_I terminalsignal) outputted from the AGC control section 25.

[0113] Meanwhile, if the control voltage (“V3_I terminal signal)outputted from the AGC control section 20 is greater than the controlvoltage (“V2_I terminal signal) outputted from the AGC control section25, the AGC response control section 26 controls the AGC amplifier 4 byusing the control voltage (“V2_I terminal signal) outputted from the AGCcontrol section 25.

[0114] That is, the AGC response control section 26 selects a controlsignal capable of lowering the gain of the AGC amplifier 4 and outputsthe control signal to the AGC amplifier 4.

[0115] Accordingly, if the levels of the in-band signals of the I-sidechannel filter 10 and the Q-side channel filter 11 are lower than thelevels of out-of-band signals of the filter inputted into the automaticgain controller, the AGC response control section 26 may control the AGCamplifier 4 by means of the control voltage outputted from the AGCcontrol section 20, which is dependent on the overall signal levelincluding out-of-band signals of the filter, so that the control voltageoutputted from the AGC control section 25 may restrict an increase ofthe gain of the AGC amplifier 4 which is required to increase the levelof the in-band signal of the I-side channel filter 10 and the Q-sidechannel filter 11 to a predetermined level. Thus, the overall signallevel including the out-of-band signals of the filter can be restrictedwithin a predetermined value.

[0116] Therefore, signal saturation of the AGC amplifier created at thefront ends of the I-side channel filter 10 and the Q-side channel filter11 due to out-of-band signals of the filter or signal distortion causedby characteristics of a non-linear area of the AGC amplifier can beprevented. In addition, if the gain of the AGC amplifier 4 is restrictedby means of the control voltage outputted from the AGC control section20, the AGC loop is operated with the signal level including out-of-bandsignals of the filter, so a level of an object signal is lowered ascompared with an original signal level thereof At this time, the levelof the object signal is compensated by a gain control of the I-side AGCamplifier 12 and the Q-side amplifier 13 installed at the rear ends ofthe I-side channel filter 10 and the Q-side channel filter 11 so thatthe original signal level is outputted.

[0117] G. Variation of Response Speed of AGC Control Section

[0118] If it is unnecessary for the first AGC loop including the I-sideAGC amplifier 12, the Q-side AGC amplifier 13, the AGC detector 14 andthe AGC control section 23 to perform a high-speed response with respectto the output signal of the AGC amplifier 4, the first AGC loop can copycontrol information of the second AGC loop, which performs the low-speedresponse with low signal distortion and includes the I-side AGCamplifier 15, the Q-side AGC amplifier 16, the AGC detector 17 and theAGC control section 25, thereby lowering the response characteristic ofthe first AGC loop and reducing signal distortion thereof

[0119] In detail, if the AGC response control section 26 is satisfiedwith the following three conditions (AND conditions), “1” is outputtedto the “Reg_Ld terminal”, the control signal of the AGC control section25 is inputted into the “Reg_In terminal” of the AGC control section 23from the “Reg_Out terminal” of the AGC control section 25, and the AGCcontrol section 23 outputs the control signal to the “Out terminal”.

[0120] (Condition 1)

[0121] A strong signal may exist out of a filter band, and the variationdegree of a signal outputted from the “Va_O terminal” is at least lowerthan the reference value “Va Delta Ref.”, even if the control voltage(“V3_I terminal signal”) outputted from the AGC control section 20 islower than the control voltage (“V2_I terminal signal”) outputted fromthe AGC control section 25.

[0122] Otherwise, a strong signal out of the filter band may not existand the control voltage (“V2_I terminal signal”) outputted from the AGCcontrol section 25 is lower than the control voltage (“V3_I terminalsignal”) outputted from the AGC control section 20.

[0123] (Condition 2)

[0124] Signal variation in the filter is very small, and a differentialvalue between the control voltage (“V1_I terminal signal”) outputtedfrom the AGC control section 23 and the control voltage (“V2_I terminalsignal”) outputted from the AGC control section 25 is lower than thereference value “V1 V2 Diff Ref.” outputted from the V1−V2 differentialvalue register 315.

[0125] (Condition 3)

[0126] The control signal is received in second AGC loop performing thelow-speed response and including the I-side AGC amplifier 15, the Q-sideAGC amplifier 16, the AGC detector 17 and the AGC control section 25,and the signal inputted into the “Sdet_I terminal” is higher than thereference value “Slow Ref−” and is lower than the reference value “SlowRef+”.

[0127] H. Gain Distribution Control Based on Variation of ReferenceValue

[0128] When it is possible to obtain quality information of a receivedsignal from a signal demodulation section connected to a rear end of theautomatic gain controller, it is necessary to prevent signal receivingperformance from deterioration caused by the signal distortion and aninferior SNR (signal to noise ratio). In addition, it is necessary toupdate the reference value “Ref3” outputted from the reference valueregister 18 and subtracted from the output signal of the AGC detector 9by means of the subtractor 19 based on obtained quality information andto perform a level distribution control with respect to the AGCamplifiers installed at front and rear ends of the I-side channel filter10 and the Q-side channel filter 11.

[0129] In detail, the control section (not shown) controlling thefunction block 27 and updating the reference value of each referencevalue register or internal register values determining the responsecharacteristic of each AGC control section, obtains quality informationof the received signal, such as a BER (bit error rate) of the receivedsignal, the SNR and a constellation of a signal, and calculates a meanvalue of quality information of the received signal.

[0130] At this time, if the mean value of the BER is less than thereference value “Ref4” and a bad BER is represented, and if a bad SNR isrepresented when the SNR is less than the reference value “Ref5”, it isdetermined that the bad BER is derived from an insufficient SNR so thatan output signal level of the AGC amplifier 4 must be maximized and thereference value “Ref3” is changed.

[0131] In detail, if the control voltage (“V3_I terminal signal)outputted from the AGC control section 20 is less than the controlvoltage (“V1_I terminal signal) outputted from the AGC control section23, and at the same time, if the control voltage (“V1_I terminal signal)outputted from the AGC control section 23 or the RSSI signal calculatedfrom the AGC response control section 26 is greater than the referencevalue “Ref6”, the reference value “Ref3” is increased so as to raise theoutput signal level of the AGC amplifier 4.

[0132] Meanwhile, if the SNR is higher than the reference value “Ref5”under the condition that the mean value of the BER is less than thereference value “Ref4“representing the bad BER, and the constellation isgreater than the reference value “Ref7” occurring with great distortion,it is determined that the signal distortion occurs in the AGC amplifier4 or in the A/D converter 5, so that the output signal level of the AGCamplifier 4 must be minimized and the reference value “Ref3” is changed.

[0133] In detail, if the control voltage (“V3_I terminal signal)outputted from the AGC control section 20 is less than the controlvoltage (“V1_I terminal signal) outputted from the AGC control section23, and at the same time, if the control voltage (“V1_I terminal signal)outputted from the AGC control section 23 or the RSSI signal calculatedfrom the AGC response control section 26 is less than the referencevalue “Ref6”, the reference value “Ref3” is decreased so as to reducethe output signal level of the AGC amplifier 4.

[0134] Accordingly, the gain distribution control at front and rear endsof the I-side channel filter 10 and the Q-side channel filter 11 iscarried out in match with a PAR (peak to average ratio) of theout-of-band signals and variation of a signal receiving status caused bya paging in such a manner that the signal receiving performance isprevented from deterioration caused by the signal distortion and the badSNR, thereby effectively utilizing a limited dynamic range.

[0135] I. Method of Changing Gain Distribution by Using Function Block

[0136] The level distribution control for the AGC amplifiers installedat front and rear ends of the I-side channel filter 10 and the Q-sidechannel filter 11 can be carried out by changing a function FN(x)according to levels of signals inputted into the automatic gaincontroller of the present invention, that is according to a ratio oflevels of in-band signals of the I-side channel filter 10 and the Q-sidechannel filter 11 to levels of out-of-band signals of the filter byusing the function block 27.

[0137] In detail, the function FN(x) may be represented as a simple gainor as a poly-nominal expression. First, a case in which the FN(x) is thesimple gain will be described.

[0138] If the function FN(x) is a simple gain, the function FN(x)satisfies the following Equations 3 and 4.

Y=ax  Equation 3

[0139] Wherein, “a” is equal to or greater than “1”.

Y=x+a  Equation 4

[0140] Wherein, “a” is greater than “−1” and less than “1”.

[0141] At this time, in the control section (not shown) controlling thefunction block 27 and updating the reference value of each referencevalue register or internal register values determining the responsecharacteristic of each AGC control section, if a status continuouslyoccurs, in which the control voltage (“V3_I terminal signal) outputtedfrom the AGC control section 20 is less than the control voltage (“V1_Iterminal signal) outputted from the AGC control section 23, and at thesame time, the control voltage (“V1_I terminal signal) outputted fromthe AGC control section 23 or the RSSI signal calculated from the AGCresponse control section 26 is less than the reference value “Ref6”, thenumber of such statuses is counted. In addition, if the number of suchstatuses per a predetermined time exceeds a predetermined number, acoefficient “a” of the above function FN(x) is decreased.

[0142] Meanwhile, if a status continuously occurs, in which the controlvoltage (“V3_I terminal signal) outputted from the AGC control section20 is less than the control voltage (“V1_I terminal signal) outputtedfrom the AGC control section 23, and at the same time, the controlvoltage (“V1_I terminal signal) outputted from the AGC control section23 or the RSSI signal calculated from the AGC response control section26 is greater than the reference value “Ref6”, the number of suchstatuses is counted. In addition, if the number of such statuses per apredetermined time exceeds a predetermined number, a coefficient “a” ofthe above function FN(x) is increased.

[0143] In addition, if the function FN(x) is represented as thepoly-nominal expression, the function FN(x) satisfies the followingEquation 5.

Y=a 0+a 1 x+a 2 x ² +a 3 x ³  Equation 5

[0144] Wherein, each coefficient of a0 to a3 is assigned from indexnumbers shown in following Table 1. In addition, FIG. 8 represents acharacteristic of different functions FN(x) according to each indexnumber. TABLE 1 Index number Coefficient 1 2 3 4 A0 −0.0094 0.0 0.0140−0.0048 A1 0.4129 0.1 0.8654 1.4620 A2 2.4606 0.0 1.4423 0.3884 A3−1.8632 0.0 −1.3112 −0.8557

[0145] At this time, in the control section (not shown) controlling thefunction block 27 and updating the reference value of each referencevalue register or internal register values determining the responsecharacteristic of each AGC control section, if a status continuouslyoccurs, in which the control voltage (“V3_I terminal signal) outputtedfrom the AGC control section 20 is less than the control voltage (“V1_Iterminal signal) outputted from the AGC control section 23, and at thesame time, the control voltage (“V1_I terminal signal) outputted fromthe AGC control section 23 or the RSSI signal calculated from the AGCresponse control section 26 is less than the reference value “Ref6”, thenumber of such statuses is counted. In addition, if the number of suchstatuses per a predetermined time exceeds a predetermined number, theindex number determining the coefficient of the above function FN(x) isdecreased.

[0146] Meanwhile, if a status continuously occurs, in which the controlvoltage (“V3_I terminal signal) outputted from the AGC control section20 is less than the control voltage (“V1_I terminal signal) outputtedfrom the AGC control section 23, and at the same time, the controlvoltage (“V1_I terminal signal) outputted from the AGC control section23 or the RSSI signal calculated from the AGC response control section26 is greater than the reference value “Ref6”, the number of suchstatuses is counted. In addition, if the number of such statuses per apredetermined time exceeds a predetermined number, a coefficient “a” ofthe above function FN(x) is increased.

[0147] Accordingly, when the input level is low, the gain of the AGCamplifier installed at the front ends of the I-side channel filter 10and the Q-side channel filter 11 is set to a higher level, therebyimproving the SNR. In addition, if the input level is high, the gain ofthe AGC amplifier installed at the front ends of the I-side channelfilter 10 and the Q-side channel filter 11 is set to a lower level,thereby compensating for the distortion generated from the AGCamplifier. In addition, in an area in which the distortion or the SNRcauses a problem, the gain characteristic of the AGC amplifier installedat the front ends of the I-side channel filter 10 and the Q-side channelfilter 11 becomes smooth so that the response characteristic of the AGCamplifier becomes slow and the re-modulation distortion of the AGC loopis reduced.

[0148] J. Calculation of RSSI

[0149] When the gain control for the AGC amplifier 4 is carried out bymeans of the control voltage outputted from the AGC control section 25,the level of the in-band object signal of a channel filter can bedetected based on the control voltage outputted from the AGC controlsection 23 or the AGC control section 25.

[0150] In addition, when the gain control for the AGC amplifier 4 iscarried out by means of the control voltage outputted from the AGCcontrol section 20, the gain of the AGC amplifier 4 is decreased inaccordance with a level of a non-object out-of-band signal of thechannel filter. Therefore, in order to set the level of the objectsignal to a predetermined level, the AGC control section 23 may increasethe gains of the I-side AGC amplifier 12 and the Q-side AGC amplifier13.

[0151] For this reason, the level of the in-band objective signal of thechannel filter band cannot be detected by means of the control voltageoutputted from the AGC control section 23 or the AGC control section 25.In this case, the level of the in-band signal of the objective band canbe obtained by compensating for an amount of gain variation of the AGCamplifier 4 based on the control voltage outputted from the AGC controlsection 23 or the AGC control section 25 and the control voltageoutputted from the AGC control section 20.

[0152] In detail, in the AGC response control section 26, if controlsignals created from the AGC control sections 20 and 25 are controlvoltages V3 and V1, and at the same time, if an overall gaincharacteristic with respect to the control voltage V1 is G(V1) and again characteristic of front circuits of the I-side channel filter 10and the Q-side channel filter 11 with respect to the control voltage V1is G3(V1), the control voltage V1 becomes the strength of an in-bandsignal of the channel filter when the control voltage V3 is greater thanthe control voltage V1. In addition, when the control voltage V3 is lessthan the control voltage V1, a calculating value V is obtained as thestrength of the in-band signal of the channel filter and is outputtedfrom the RSSI terminal according to Equation 6:

V=V 1+(G 3(V 1)/G(V 1))(V 1−V 3)  Equation 6

[0153] As described above, the automatic gain controller according tothe first embodiment of the present invention includes the AGC amplifier4 installed at front ends of the I-side channel filter 10 and the Q-sidechannel filter 11. In addition, the I-side AGC amplifier 12, the Q-sideAGC amplifier 13, the I-side AGC amplifier 15 and the Q-side AGCamplifier 16 are installed at rear ends of the I-side channel filter 10and the Q-side channel filter 11.

[0154] In addition, the AGC detector 9 detects the output signal of theAGC amplifier 4 at the front ends of the I-side channel filter 10 andthe Q-side channel filter 11, and at the same time, the AGC detector 14detects the output signals of the I-side AGC amplifier 12 and the Q-sideAGC amplifier 13 and the AGC detector 15 detects the output signals ofthe I-side AGC amplifier 15 and the Q-side AGC amplifier 16 at the rearends of the I-side channel filter 10 and the Q-side channel filter 11.

[0155] If out-of-band signals of the I-side channel filter 10 and theQ-side channel filter 11 are strong, the gain control for the AGCamplifier 4 is carried out based on the control signal of the AGCcontrol section 20 by using the signal detected by the AGC detector 9.In addition, if out-of-band signals of the I-side channel filter 10 andthe Q-side channel filter 11 are weak, the gain control for the AGCamplifier 4 is carried out based on the control signal of the AGCcontrol section 25 by using the signal detected by the AGC detector 17.

[0156] In addition, output signals of the I-side AGC amplifier 12 andthe Q-side AGC amplifier 13 controlled by the AGC control section 23having a rapid response speed are utilized as output signals of theautomatic gain controller. If level variation of the output signal ofthe AGC amplifier 4 is stable, the control signal of the AGC controlsection 23 is identical to the control signal of the AGC control section25.

[0157] Accordingly, the automatic gain controller according to the firstembodiment of the present invention can properly carry out the automaticgain control in accordance with the variation of the out-of-band signalsof the channel filter extracting the object signal, effectively utilizea limited dynamic range, and prevent signal saturation at the front endof the channel filter. In addition, if the signal variation is verysmall at the front end of the channel filter, the response speed of theAGC amplifier installed at the rear end of the channel filter becomesslow, so that the object signal is prevented from distortion caused bythe rapid AGC response.

Embodiment 2

[0158] Hereinafter, an automatic gain controller according to a secondembodiment of the present invention will be described.

[0159] A. Structure

[0160]FIG. 9 is a block diagram showing a structure of a wirelessapparatus having an automatic gain controller according to the secondembodiment of the present invention. The automatic gain controlleraccording to the second embodiment is different from the automatic gaincontroller according to the first embodiment in that the automatic gaincontroller according to the first embodiment performs an orthogonaldetection for a signal received in the front end of the channel filterextracting the object signal, and the automatic gain controlleraccording to the second embodiment performs the orthogonal detection fora signal received in the channel filter and for a signal receivedrearward of the AGC amplifier installed at the rear end of the channelfilter, and the AGC detection is carried out with an absolute value of areal signal.

[0161] Therefore, the second embodiment will be described with regard todifferent parts between the automatic gain controller of the firstembodiment and the automatic gain controller of the second embodiment.In FIG. 9, the parts having the same reference numerals as the parts ofFIG. 1 have the same functions and structures as those of the partsshown in FIG. 1, so they will not be further described below.

[0162] In addition, according to the automatic gain controller of thepresent invention, if an IF frequency of a received signal is lower thana half of a sampling frequency of the A/D converter 5, sample points perone period of a signal are densely formed, so a level detection errorcaused by a differential phase condition between the signal and thesample points will be reduced.

[0163] In detail, as shown in FIG. 9, the signal inputted into the mixer1 from the RF/IF terminal is converted into a signal having a lowfrequency (input IF frequency of the A/D converter 5) in the mixer 1 byusing a local signal having a first frequency, which is outputted from alocal oscillator 2. Then, a signal having a predetermined frequency bandis extracted from the signal outputted from the mixer 1 by using abandpass filter 3.

[0164] An AGC amplifier 4 is a variable gain amplifier for converting anoutput signal of the bandpass filter 3 into a signal having a constantlevel. The signal having the predetermined frequency band, which isconverted into the signal having the constant level by the AGC amplifier4, is inputted into the A/D converter 5 so that the signal is convertedinto a quantizing digital signal by means of the A/D converter 5.

[0165] The quantizing digital signal having an IF frequency is inputtedinto an AGC detector 30, converted into a band signal of an objectiveband due to the band of the quantizing digital signal being limited by achannel filter 31, and is inputted into an AGC amplifier 32. In order tocreate a gain control signal for the AGC amplifier 4, the AGC detector30 calculates an absolute value of the inputted IF frequency signal andintegrates the absolute value, thereby detecting variation of an outputsignal of the A/D converter 5.

[0166] In addition, the AGC amplifier 32 is a variable gain amplifierfor converting an output signal of the channel filter 31 into a signalhaving a constant level. The band signal of the objective band, which isconverted into the signal having the constant level by the AGC amplifier32, is subject to an orthogonal detection. The orthogonal detection iscarried out by using a local signal (cosine wave in I-side and −sinewave in Q-side) having a second frequency outputted from a digital localoscillator 38 of an I-side mixer 36 and a Q-side mixer 37 and isconverted into a complex number signal having a baseband frequencyrepresented by an I-axis signal and a Q-axis signal. In addition, thesignal is outputted from the wireless apparatus as complex numbersignals BB.I and BB.Q having baseband frequencies.

[0167] In addition, the band signal of the objective band, which isconverted into the signal having the constant level by the AGC amplifier32, is inputted into an AGC detector 33. In order to create a gaincontrol signal for the AGC amplifier 32, the AGC detector 33 calculatesan absolute value of the inputted band signal of the objective band andintegrates the absolute value, thereby detecting variation of an outputsignal of the AGC amplifier 32.

[0168] In the same manner, the signal converted into the band signal ofthe objective band and band-limited by the channel filter 31 is inputtedinto an AGC amplifier 34. The AGC amplifier 34 is a variable gainamplifier for converting an output signal of the channel filter 31 intoa signal having a constant level. The band signal of the objective band,which is converted into the signal having the constant level by the AGCamplifier 34, is inputted into an AGC detector 35.

[0169] In order to create a gain control signal for the AGC amplifier34, the AGC detector 35 calculates an absolute value of the inputtedband signal of the objective band and integrates the absolute value,thereby detecting variation of an output signal of the AGC amplifier 34.

[0170] The AGC detectors 30, 33 and 35 will be described in detaillater.

[0171] Meanwhile, in order to create signals for controlling the gain ofeach AGC amplifier, output signals of the AGC detectors 30, 33 and 35are inputted into an AGC control section creating a gain control signalfor each AGC amplifier. In detail, a reference value Ref3 outputted froma reference value register 18 is subtracted from an output signal of theAGC detector 30 by means of a subtractor 19 and a result thereof isinputted into an “In terminal” of an AGC control section 20.

[0172] In addition, a reference value Ref1 outputted from a referencevalue register 21 is subtracted from an output signal of the AGCdetector 33 by means of a subtractor 22 and a result thereof is inputtedinto an “In terminal” of an AGC control section 23. Also, the referencevalue Ref1 outputted from the reference value register 21 is subtractedfrom an output signal of the AGC detector 35 by means of a subtractor 24and a result thereof is inputted into an “In terminal” of an AGC controlsection 25 having response characteristic lower than responsecharacteristic of the AGC control section 23.

[0173] Other connection structures of the automatic gain controlleraccording to the second embodiment of the present invention are similarto those of the automatic gain controller according to the firstembodiment of the present invention, so they will not be furtherdescribed below.

[0174] B. AGC Detector

[0175] Hereinafter, AGC detectors 30, 33 and 35 of the automatic gaincontroller according to the second embodiment will be described indetail with reference to accompanying drawings. The AGC detectors 30, 33and 35 have the same structure with each other, and FIG. 10 shows astructure of a real input type AGC detector.

[0176] Referring to FIG. 10, as a signal is inputted through an “Interminal”, an absolute value calculator 401 calculates an absolute valueof the signal. An output signal of the absolute value calculator 401 issimultaneously inputted into a comparator 402 and an integrator 403including a multiplier 403 a, an adder 403 b, a delay unit 403 c, amultiplier 403 d, and a coefficient calculator 403 e.

[0177] Herein, the integrator 403 is designed to integrate the outputsignal of the absolute value calculator 401 based on any one of anattack coefficient outputted from an attack coefficient register 406 anda release coefficient outputted from a release coefficient register 405(wherein, an attack coefficient value is larger than a releasecoefficient value), which are selected by a switch 404 controlled bymeans of an output signal of the comparator 402. In detail, the outputsignal of the absolute value calculator 401 inputted into the integrator403 is multiplied by one of the attack coefficient and the releasecoefficient, which are inputted into the integrator 403 as numeratorcoefficients, by means of the multiplier 403 a.

[0178] In addition, a denominator coefficient of the attack coefficientor the release coefficient inputted into the integrator 403 iscalculated by means of the coefficient calculator 403 e. An outputsignal of the coefficient calculator 403 e is multiplied by an outputsignal of the integrator 403 through the multiplier 403 d and the resultthereof is added to an output signal of the multiplier 403 a by means ofthe adder 403 b. Meanwhile, an output signal of the adder 403 b isoutputted through an “Out terminal” via the delay unit 403 c as anoutput signal of the integrator 403, that is, as an output signal of theAGC detector.

[0179] The comparator 402 compares the output signal of the absolutevalue calculator 401 with an output signal of the multiplier 403 d. Ifthe output signal of the absolute value calculator 401 is smaller thanthe output signal of the multiplier 403 d, the switch 404 selects therelease coefficient so as to enlarge an integration time constant. Ifthe output signal of the absolute value calculator 401 is larger thanthe output signal of the multiplier 403 d, the switch 404 selects theattack coefficient so as to reduce the integration time constant. Thus,the output signal level of the integrator 403 may be between aneffective value and a peak value of an input signal. In addition, theattack coefficient value is larger than the release coefficient value.As a differential value between the attack coefficient value and therelease coefficient value becomes large, the output signal of theintegrator 403 may be close to the peak value.

[0180] In addition, an orthogonal detector extracts an envelope of areceived signal by using an analog mixer.

[0181] The AGC detector 30 rectifies a signal by using a diode and candetect a level of the received signal.

[0182] As described above, the automatic gain controller according tothe second embodiment performs the orthogonal detection for a signalreceived in the channel filter and for a signal received rearward of theAGC amplifier installed at the rear end of the channel filter.Therefore, the envelope of the signal can be obtained by calculating theabsolute value of the signal using the AGC detector. In addition, theautomatic gain controller can properly carry out the automatic gaincontrol in accordance with variations of the out-of-band signals of thechannel filter extracting the object signal, and can effectively utilizea limited dynamic range. In order to restrict the level variation in theAGC detector 30, it is necessary to enlarge a ratio of the samplingfrequency to a signal frequency.

[0183]FIGS. 11A to 11K are views showing a response waveform in eachpart of the automatic gain controller according to the second embodimentof the present invention. FIG. 11A represents an out-of-band signal ofchannel filter 31, FIG. 11B represents an in-band signal of channelfilter 31, FIG. 11C represents an output signal of A/D converter 5, FIG.11D represents an output signal of an automatic gain controller, FIG.11E represents a “Va_O terminal” output signal of AGC response controlsection 26, FIG. 11F represents an “Out terminal” output signal of AGCcontrol section 20, FIG. 11G represents a “Csa terminal” output signalof AGC response control section 26 (wherein, a “Csa terminal” of AGCresponse control section 26 is an output terminal of comparator 301connected to switch 302 and OR circuit 310 shown in FIG. 4), FIG. 11Hrepresents an “Out terminal” output signal of AGC control section 25,FIG. 11I represents an “Out terminal” output signal of AGC controlsection 23, FIG. 11J represents a “Reg_Ld terminal” output signal of AGCresponse control section 26, and FIG. 11K represents a “RSSI terminal”output signal of AGC response control section 26.

[0184] Referring to FIGS. 11A to 11K, when an in-band signal of thechannel filter 31 is inputted at a first time t1, since the responsecharacteristic of the AGC control section 25 is slower than the responsecharacteristic of the AGC control section 20, the “Out terminal” outputsignal of the AGC control section 20 is outputted through a “Va_Oterminal” of the AGC response control section 26 by means of the “Csaterminal” output signal of the AGC response control section 26. At thistime, since the out-of-band signal of the channel filter 31 has not beeninputted, the “Out terminal” output signal of the AGC control section 25is directly outputted through the “Va_O terminal” of the AGC responsecontrol section 26 at a second time t2, in which the AGC control section25 reacts with the response of the AGC control section 20.

[0185] Meanwhile, when the output signal of the A/D converter 5 has beenstabilized, control information of the AGC control section 25 is copiedin the AGC control section 23 at a third time t3 by means of a “C1_Oterminal” output signal of the AGC response control section 26. Thus,the “Out terminal” output signal of the AGC control section 25represents the response characteristic identical to the responsecharacteristic of the “Out terminal” output signal of the AGC controlsection 23. In addition, at a fourth time t4, the AGC control section 23operates separately from the AGC control section 25 in order to rapidlyincrease the gain of the AGC amplifier 32 to match with the stop of thein-band signal of the channel filter 31.

[0186] In addition, at a fifth time t5, the “Out terminal” output signalof the AGC control section 20 is outputted through the “Va_O terminal”of the AGC response control section 26 by means of the “Csa terminal”output signal of the AGC response control section 26 to match with aninput of the out-of-band signal of the channel filter 31. At this time,the output signal of the automatic gain controller includes “ringing”from the channel filter 31 caused by the out-of-band signal of thechannel filter 31 even though the in-band signal of the channel filter31 is in a stop state. This is because weak signals of a channel bandmust have a predetermined level, the AGC amplifier 32 achieves a highgain due to a high-speed response, and the ringing from the channelfilter 31 becomes a visible amplitude level.

[0187] Then, at a sixth time t6, since the out-of-band signal of thechannel filter 31, which has a level stronger than a level of thein-band signal, has been already inputted, the “Csa terminal” outputsignal of the AGC response control section 26 does not vary even if thein-band signal of the channel filter 31 is inputted. At this time, theoutput signal of the automatic gain controller includes the in-bandsignal of the channel filter 31. Although the out-of-band signal of thechannel filter 31 has been already inputted, if the output signal of theA/D converter 5 is stabilized, control information of the AGC controlsection 25 can be copied in the AGC control section at a seventh time t7by means of the “Reg_Ld terminal” output signal of the AGC responsecontrol section 26. Thus, the “Out terminal” output signal of the AGCcontrol section 25 represents the response characteristic identical tothe response characteristic of the “Out terminal” output signal of theAGC control section 23.

[0188] In addition, at an eighth time t8, the AGC control section 23operates separately from the AGC control section 25 in order to rapidlyincrease the gain of the AGC amplifier 32 to match with the stop of thein-band signal of the channel filter 31. At this time, the output signalof the automatic gain controller includes “ringing” from the channelfilter 31 caused by the out-of-band signal of the channel filter 31 eventhough the in-band signal of the channel filter 31 is in a stop state.This is because weak signals of a channel band must have a predeterminedlevel, the AGC amplifier 32 achieves a high gain due to a high-speedresponse, and the ringing from the channel filter 31 becomes a visibleamplitude level.

Embodiment 3

[0189] Hereinafter, an automatic gain controller according to a thirdembodiment of the present invention will be described.

[0190] A. Structure

[0191]FIG. 12 is a block diagram showing a structure of a wirelessapparatus having the automatic gain controller according to the thirdembodiment of the present invention. The automatic gain controlleraccording to the third embodiment is different from the automatic gaincontroller according to the second embodiment in that the automatic gaincontroller according to the second embodiment performs the gain controlfor the AGC amplifier, which is installed at the front end of thechannel filter extracting the object signal, in an IF frequency bandrearward of the mixer, and the automatic gain controller according tothe third embodiment performs the gain control in an RF/IF frequencyband forward of the mixer.

[0192] Therefore, the third embodiment will be described with regard todifferent parts between the automatic gain controller of the secondembodiment and the automatic gain controller of the third embodiment. InFIG. 12, the parts having the same reference numerals as the parts ofFIG. 9 have the same functions and structures as those of the partsshown in FIG. 9, so they will not be further described below.

[0193] In detail, as shown in FIG. 12, a signal inputted from an RF/IFterminal is inputted into an AGC amplifier 39. A gain control for theAGC amplifier 39 is carried out by means of an output signal of a D/Aconverter 28. The AGC amplifier 39 is a variable gain amplifier forsetting a level of an input signal inputted into a mixer 1 to apredetermined level. The input signal, which is converted into thesignal having the predetermined level by the AGC amplifier 39, isinputted into the mixer 1. Then, the input signal is converted into asignal having a low frequency (input IF frequency of the A/D converter 5installed at a rear end) in the mixer 1 by using a local signal having afirst frequency, which is outputted from a local oscillator 2. Then, asignal having a predetermined frequency band is extracted from thesignal outputted from the mixer 1 by using a bandpass filter 3.

[0194] For instance, the AGC amplifier 39 can be realized by varying anattenuation degree of a pin diode by restricting voltage applied to thepin diode.

[0195] Meanwhile, the input signal, which is converted into the signalhaving a predetermined level by the AGC amplifier 39, is inputted intoan AGC detector 40. In order to create a gain control signal for the AGCamplifier 39, the AGC detector 40 detects variation of an output signalof the AGC amplifier 39 by rectifying the output signal of the AGCamplifier 39 through a diode. Since the AGC detector 40 creates the gaincontrol signal for the AGC amplifier 39, the output signal of the AGCdetector 40 is quantized and converted into a digital signal through anA/D converter 41. Then, a reference value Ref3 outputted from areference value register 18 is subtracted from the output signal of theAGC detector 40 by means of a subtractor 19 and a result thereof isinputted into an “In terminal” of the AGC control section 20.

[0196] Other connection structures of the automatic gain controlleraccording to the third embodiment of the present invention are similarto those of the automatic gain controller according to the secondembodiment of the present invention, so they will not be furtherdescribed below.

[0197] As described above, the automatic gain controller according tothe third embodiment of the present invention performs the gain controlat the front end of the channel filter extracting the object signal inthe RF frequency band. Therefore, as the same as the automatic gaincontroller according to the first embodiment of the present invention,the automatic gain controller according to the third embodiment of thepresent invention can properly perform the automatic gain control tomatch with variations of the out-of-band signal of the channel filterextracting the object signal. In addition, the automatic gain controlleraccording to the third embodiment of the present invention caneffectively utilize a limited dynamic range and can prevent signalsaturation at the front end of the channel filter while restrictingsignal distortion in the RF frequency band. In a case of a receiver, inwhich the IF frequency is not converted into a digital signal, thesignal distortion can be reduced at the front end of the channel filter.

Embodiment 4

[0198] Hereinafter, an automatic gain controller according to a fourthembodiment of the present invention will be described.

[0199] A. Structure

[0200]FIG. 13 is a block diagram showing a structure of a wirelessapparatus having an AGC according to the fourth embodiment of thepresent invention. The automatic gain controller according to the fourthembodiment is different from the automatic gain controller according tothe first embodiment in that the automatic gain controller according tothe first embodiment includes the first AGC loop and the second AGC loopat rear ends of the I-side channel filter 10 and the Q-side channelfilter 11, and an output signal of the automatic gain controller isextracted from the first AGC loop, in which the first AGC loop has theI-side AGC amplifier 12, the Q-side AGC amplifier 13, the AGC detector14 and the AGC control section 23 and performs a high-speed response.The second AGC loop of the first embodiment has the I-side AGC amplifier15, the Q-side AGC amplifier 16, the AGC detector 17 and the AGC controlsection 25 and performs a low-speed response with a low signaldistortion. However, the automatic gain controller according to thefourth embodiment does not have a second AGC loop including the I-sideAGC amplifier 15, the Q-side AGC amplifier 16, the AGC detector 17 andthe AGC control section 25.

[0201] In detail, according to the automatic gain controller of thefourth embodiment, the I-side AGC amplifier 15, the Q-side AGC amplifier16, the AGC detector 17 and the AGC control section 25 shown in FIG. 1are omitted. In addition, the output signal of the AGC control section23 is not inputted into the “V1_I terminal”, but inputted into the “V2-Iterminal” of the AGC response control section 26. Furthermore, the timeconstant of response characteristic of the AGC control section in theautomatic gain controller of the fourth embodiment is identical to thetime constant of the response characteristic of the AGC control section25 in the automatic gain controller of the first embodiment.

[0202] As described above, the automatic gain controller according tothe fourth embodiment of the present invention omits the second AGC loopincluding the I-side AGC amplifier 15, the Q-side AGC amplifier 16, theAGC detector 17 and the AGC control section 25, which are provided inthe automatic gain controller according to the first embodiment of thepresent invention. Therefore, as the same as the automatic gaincontroller according to the first embodiment of the present invention,the automatic gain controller according to the fourth embodiment of thepresent invention can properly perform the automatic gain control tomatch with variations of the out-of-band signal of the channel filterextracting the object signal, while minimizing signal processing at therear end of the channel filter. In addition, the automatic gaincontroller according to the fourth embodiment of the present inventioncan effectively utilize a limited dynamic range and can prevent signalsaturation at the front end of the channel filter.

Embodiment 5

[0203] Hereinafter, the characteristic of the automatic gain controllersaccording to the first to fourth embodiments of the present inventionwill be described with reference to FIGS. 14 and 15. FIG. 14 is a graphshowing an example of a gain characteristic of an AGC amplifier as afunction of control voltage when the AGC amplifier is installed at therear end of the channel filter. According to the characteristic of theAGC amplifier shown in FIG. 14, the gain is constantly maintained at −25[dB] when the control voltage is below 0.0, and is constantly maintainedat 25 [dB] when the control voltage is above 0.5. In addition, when thecontrol voltage is in a range between 0.0 and 0.5, the gain increases by10 [dB] as the control voltage increases by 0.1 and the gain becomes 0[dB] when the control voltage is 0.25.

[0204]FIG. 15 is a graph showing an example of a gain characteristic ofthe AGC amplifier as a function of control voltage when the AGCamplifier is installed at the front end of the channel filter. Accordingto the characteristic of the AGC amplifier shown in FIG. 15, the gain isconstantly maintained at −35 [dB] when the control voltage is below 0.5,and is constantly maintained at 15 [dB] when the control voltage isabove 1.0. In addition, when the control voltage is in a range between0.5 and 1.0, the gain increases by 10 [dB] as the control voltageincreases by 0.1 and the gain becomes 0 [dB] when the control voltage is0.85.

[0205] If the gain characteristic of the AGC amplifiers according tofirst to the fourth embodiments of the present invention is formedidentical to the gain characteristic shown in FIGS. 14 and 15, it ispossible to prevent the SNR from deterioration caused by an inferior NF(noise figure) by maintaining the gain of the AGC amplifier, which isinstalled at the front end of the channel extracting the object signal,at a high level when a small amount of signals is inputted. However, ifthe gain of the AGC amplifier, which is installed at the front end ofthe channel extracting the object signal, is maintained at the highlevel, signal saturation may occur due to the out-of-band signals of thechannel filter.

[0206] Accordingly, when the AGC amplifiers having the above-mentionedresponse characteristic are provided in the automatic gain controllersaccording to the first to fourth embodiments of the present invention,it is necessary to adjust the gain of the AGC amplifier installed at thefront end of the channel filter in such a manner that signal saturationdoes not occur when a small amount of signals is inputted. At this time,the control voltage of the AGC control section for each AGC amplifier isabove 0.5.

[0207] In addition, when a large amount of signals is inputted, the gainof the AGC amplifier installed at the front end of the channel filtermust be minimized and gain control is carried out by means of the AGCamplifier installed at the rear end of the channel filter in order toraise the signal level, which has been dropped by means of the AGCamplifier installed at the front end of the channel filter. At thistime, the control voltage of the AGC control section for each AGCamplifier is below 0.5.

[0208] In the automatic gain controller according to the fifthembodiment of the present invention, a non-sensitive area against thecontrol voltage of the AGC control section is formed at a front portionor a rear portion of the channel filter extracting the object signal.For this reason, the response characteristic of the automatic gaincontroller according to the fifth embodiment of the present inventionmay be lowered than the automatic gain controllers according to thefirst to fourth embodiments of the present invention. However, theautomatic gain controller according to the fifth embodiment of thepresent invention can maintain a superior NF while preventing signalsaturation at the front portion of the channel filter.

Embodiment 6

[0209] In the automatic gain controllers according to the first tofourth embodiments of the present invention, the attack coefficient andthe release coefficient, which are multiplied by the input signals fromthe AGC control sections 23 and 25, are set to “0“(attackcoefficient=release coefficient=0). When quality information of areceived signal can be obtained from a signal demodulation sectionconnected to the rear end of the automatic gain controller, it isnecessary to prevent signal receiving performance from deteriorationcaused by the signal distortion and inferior SNR (signal to noiseratio). In addition, it is necessary to update the reference value“Ref1” outputted from the reference value register 21 and subtractedfrom the output signal of the AGC detector 14 or AGC detector 17 bymeans of the subtractor 22 or subtractor 24 based on obtained qualityinformation and to perform a level distribution control with respect toeach AGC amplifier.

[0210] In automatic gain controllers for controlling the gain of the AGCamplifier based on communication quality, the automatic gain controlleraccording a sixth embodiment of the present invention can prevent signalsaturation from being created at the front end of the channel filtercaused by the out-of-band signals of the channel filter extracting theobject signal.

[0211] As described above, the automatic gain controller according tothe present invention includes a first variable gain amplifying unitinstalled at the front end of the channel filter extracting the objectsignal, and second and third variable gain amplifying units installed atthe rear end of the channel filter. In addition, a control signalselecting unit is provided to select a control signal from controlsignals generated by first and second control signal generating units inorder to control the first variable gain amplifying unit, in such amanner that the first variable gain amplifying unit installed at thefront end of the filter can be controlled based on variation of thesignal inputted into the channel filter or variation of the signaloutputted from the filter. Accordingly, out-of-band signals of thefilter doe not exert an influence when a gain control is performed forthe in-band signal of the filter.

[0212] Therefore, the automatic gain controller of the present inventioncan properly carry out the automatic gain control in accordance withvariations of the out-of-band signals of the channel filter extractingthe object signal and can effectively utilize a limited dynamic rangewhile preventing signal saturation at the front end of the filter.

[0213] In addition, the second and third variable gain amplifying unitsare installed at both sides of the rear end of the filter, and the thirdvariable gain amplifying unit outputs the signal as an output signal ofthe automatic gain controller. At the same time, when the first variablegain amplifying unit installed at the front end of the channel filter iscontrolled based on variations of the signal outputted from the channelfilter by using the second control signal generating unit, controlinformation of the second control signal generating unit is copied inthe third control signal generating unit. The gain control for the thirdvariable gain amplifying unit is carried out in accordance with aresponse speed of the second control signal generating unit. Thus, theautomatic gain controller may output the signal without occurring signaldistortion.

[0214] Accordingly, when the variation of the signal at the front end ofthe channel filter is very small, the response speed of the AGCamplifier installed at the rear end of the channel filter becomes slow,so that the object signal is prevented from being distorted due to arapid AGS response.

[0215] In addition, when quality information of a received signal isobtained from a signal demodulation section connected to a rear end ofthe automatic gain controller, and when the first control signalgenerating unit generates the control signal based on a level of aninput signal, a reference value, which is compared with the level of theinput signal and is varied depending on a status of quality informationby means of a reference value varying unit, so that it is possible tobalance the influence of the out-of-band signal and the in-band signalof the filter when gain control is carried out with respect to thein-band signal of the filter.

[0216] Furthermore, the automatic gain controller of the presentinvention has a gain distribution adjusting unit. The gain distributionadjusting unit adjusts the gain distribution in a front end circuit anda rear end circuit of the filter by comparing levels of the out-of-bandsignal and the in-band signal of the filter with each other, therebyproperly distributing the gain in front and rear portions of the filter.

[0217] Accordingly, the automatic gain controller of the presentinvention can effectively utilize a limited dynamic range and canprevent the SNR from deterioration caused by an inferior NF (noisefigure) while preventing signal saturation at the front end of thechannel filter. Thus, an optical signal may be outputted from theautomatic gain controller.

[0218] In addition, the automatic gain controller of the presentinvention has a signal strength calculating unit so as to measure alevel of the object signal based on the control signal generated fromeach control signal generating unit. Thus, the automatic gain controllercan easily measure the level of the object signal based on the controlsignal generated from each control signal generating unit.

[0219] Therefore, the automatic gain controller of the present inventioncan output the optimum signal having an optimum level regardless of thestatuses of the out-of-band signal and the in-band signal of the filter.

[0220] While the invention has been shown and described with referenceto certain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

What is claimed is:
 1. An automatic gain controller comprising: a firstvariable gain amplifying means for amplifying an input signal; a filterfor limiting a band of an output signal of the first variable gainamplifying means; a second variable gain amplifying means for outputtingan output signal of the filter to an exterior by amplifying the outputsignal of the filter; a first control signal generating means generatinga first control signal for controlling a level of the output signal ofthe first variable gain amplifying means to a predetermined level; asecond control signal generating means generating a second controlsignal for controlling a level of an output signal of the secondvariable gain amplifying means to a predetermined level and outputtingthe second control signal to the second variable gain amplifying means;and a control signal selecting means selecting one of the first andsecond control signals generated from the first and second controlsignal generating means and outputting a selected control signal to thefirst variable gain amplifying means.
 2. The automatic gain controlleras claimed in claim 1, wherein the control signal selecting meanscompares the first control signal of the first control signal generatingmeans with the second control signal of the second control signalgenerating means, and at the same time, selects one of the first andsecond control signals capable of lowering a gain of the first variablegain amplifying means, and outputs the selected signal to the firstvariable gain amplifying means.
 3. The automatic gain controller asclaimed in claim 2, further comprising a reference value varying meansfor varying a reference value, which is compared with a level of aninput signal, depending on a status of quality information, when qualityinformation of a received signal is obtained from a signal demodulationsection connected to a rear end of the automatic gain controller andwhen the first control signal generating means generates the firstcontrol signal based on a level of the input signal.
 4. The automaticgain controller as claimed in claim 3, wherein the reference valuevarying means varies the reference value by comparing a level of thefirst control signal generated from the first control signal generatingmeans with a level of the second control signal generated from thesecond control signal generating means, and by comparing a level of areceived in-band signal with a predetermined value.
 5. The automaticgain controller as claimed in claim 4, further comprising a gaindistribution adjusting means for adjusting a gain distribution in afront end circuit and a rear end circuit of the filter by comparing alevel of an out-of-band signal of the filter with a level of an in-bandsignal of the filter.
 6. The automatic gain controller as claimed inclaim 5, further comprising a signal strength calculating means,wherein, if the first control signal generated from the first controlsignal generating means is control voltage V3, and the second controlsignal generated from the second control signal generating means iscontrol voltage V1, and at the same time, if an overall gaincharacteristic with respect to the control voltage V1 is G(V1) and again characteristic of the front end circuit of the filter with respectto the control voltage V1 is G3(V1), the signal strength calculatingmeans determines the control voltage V1 as a strength of an in-bandsignal of the filter when the control voltage V3 is greater than thecontrol voltage V1, and determines a calculating value V as the strengthof the in-band signal of the filter when the control voltage V3 is lessthan the control voltage V1, wherein the calculating value V satisfies:V=V 1+(G 3(V 1)/G(V 1))(V 1−V 3)
 7. An automatic gain controllercomprising: a first variable gain amplifying means for amplifying aninput signal; a filter for limiting a band of an output signal of thefirst variable gain amplifying means; a second variable gain amplifyingmeans for amplifying an output signal of the filter; a third variablegain amplifying means for outputting the output signal of the filter byamplifying the output signal of the filter; a first control signalgenerating means generating a first control signal for controlling alevel of the output signal of the first variable gain amplifying meansto a predetermined level; a second control signal generating meansgenerating a second control signal for controlling a level of an outputsignal of the second variable gain amplifying means to a predeterminedlevel and outputting the second control signal to the second variablegain amplifying means; a third control signal generating means having aresponse characteristic faster than a response characteristic of thesecond control signal generating means, generating a third controlsignal for controlling a level of an output signal of the third variablegain amplifying means to a predetermined level, and outputting the thirdcontrol signal to the third variable gain amplifying means; and acontrol signal selecting means selecting one of the first and secondcontrol signals generated from the first and second control signalgenerating means and outputting a selected control signal to the firstvariable gain amplifying means.
 8. The automatic gain controller asclaimed in claim 7, wherein each of the second and third control signalgenerating means includes a control information copying unit for copyingcontrol information of the second control signal generating means intothe third control signal generating means, and the control informationcopying unit copies control information of the second control signalgenerating means into the third control signal generating means when thecontrol signal selecting means selects the second control signalgenerated from the second signal generating means and outputs the secondcontrol signal to the first variable gain amplifying means.
 9. Theautomatic gain controller as claimed in claim 8, wherein the controlsignal selecting means allows the control information copying unit tocopy control information of the second control signal generating meansinto the third control signal generating means, when a variation valueof the first control signal generated from the first control signalgenerating means per a unit time is less than a predetermined value. 10.The automatic gain controller as claimed in claim 9, wherein the controlsignal selecting means compares the first control signal of the firstcontrol signal generating means with the second control signal of thesecond control signal generating means, and at the same time, selectsone of the first and second control signals capable of lowering a gainof the first variable gain amplifying means, and outputs the selectedsignal to the first variable gain amplifying means.
 11. The automaticgain controller as claimed in claim 10, further comprising a referencevalue varying means for varying a reference value, which is comparedwith a level of an input signal, depending on a status of qualityinformation, when quality information of a received signal is obtainedfrom a signal demodulation section connected to a rear end of theautomatic gain controller and when the first control signal generatingmeans generates the first control signal based on a level of the inputsignal.
 12. The automatic gain controller as claimed in claim 11,wherein the reference value varying means varies the reference value bycomparing a level of the first control signal generated from the firstcontrol signal generating means with a level of the second controlsignal generated from the second control signal generating means, and bycomparing a level of a received in-band signal with a predeterminedvalue.
 13. The automatic gain controller as claimed in claim 12, furthercomprising a gain distribution adjusting means for adjusting a gaindistribution in a front end circuit and a rear end circuit of the filterby comparing a level of an out-of-band signal of the filter with a levelof an in-band signal of the filter.
 14. The automatic gain controller asclaimed in claim 13, further comprising a signal strength calculatingmeans, wherein, if the first control signal generated from the firstcontrol signal generating means is control voltage V3, and the secondcontrol signal generated from the second control signal generating meansis control voltage V1, and at the same time, if an overall gaincharacteristic with respect to the control voltage V1 is G(V1) and again characteristic of the front end circuit of the filter with respectto the control voltage V1 is G3(V1), the signal strength calculatingmeans determines the control voltage V1 as a strength of an in-bandsignal of the filter when the control voltage V3 is greater than thecontrol voltage V1, and determines a calculating value V as the strengthof the in-band signal of the filter when the control voltage V3 is lessthan the control voltage V1, wherein the calculating value V satisfies:V=V 1+(G 3(V 1)/G(V 1))(V 1−V 3)